The present disclosure relates generally to a releasable connection for a downhole assembly. More particularly, the present disclosure relates to a mechanically engaged and releasable connection that may be disposed between a tool string and a downhole tool and actuated to disconnect the downhole tool from the tool string upon application of an axial load.
To form an oil or gas well, a bottom hole assembly (BHA), including components such as a motor, steering assembly and drill bit, is coupled to an end of a drillstring and then inserted downhole, where drilling commences. When forming a substantially straight borehole, the drillstring typically includes a number of pipe joints threaded end to end. Circumstances may arise in which it is desirable to disconnect the drillstring from the BHA, for example, when the BHA becomes stuck in the borehole during drilling. At such times, the drillstring is disconnected from the BHA by applying torque to the drillstring and uncoupling a threaded connection between the drillstring and the BHA. Once disconnected from the BHA, the drillstring may be extracted from the borehole and the stuck BHA subsequently retrieved via fishing, jarring or another operation.
When forming a deviated, lateral or upwardly sloping borehole, it is not economically feasible or practical to use a drillstring made from jointed pipe. Instead, the BHA may be coupled to coiled tubing, which includes one or more lengths of continuous, unjointed tubing spooled onto reels for storage in sufficient quantities to exceed the maximum length of the borehole. Because the coiled tubing cannot be disconnected from the BHA by the application of torque to the coiled tubing, an axial disconnect is positioned in the tubing string between the BHA and the coiled tubing prior to insertion of the tubing string downhole. The axial disconnect facilitates decoupling of the coiled tubing from the BHA in the event that it becomes desirable to do so, such as when the BHA becomes stuck during drilling. To decouple the BHA from the coiled tubing, the disconnect is actuated to allow the BHA to disconnect from the coiled tubing upon application of an axial load to the coiled tubing. Once disconnected from the BHA, the tubing string may be extracted from the borehole and the stuck BHA subsequently retrieved via fishing, jarring or another operation.
A variety of conventional axial disconnects have been used to decouple a coiled tubing string from a downhole tool, such as a BHA. Some conventional disconnects include locking dogs, interlocking fingers, grapples or similar devices which are actuated, such as by application of a hydraulic pressure load, to release the tool coupled thereto. One shortcoming of these disconnects is that the locking dogs, interlocking fingers, and grapples are relatively weak components, in comparison to the other components of the disconnect. Another shortcoming is that the disconnects are usually thin-walled. Both design characteristics limit the loads which may be safely applied to the disconnects. Other conventional disconnects may be capable of handling higher loads. However, those disconnects are typically very sophisticated tools, having many working parts, each representing a potential failure point and increased manufacturing cost. These disconnects may also include expensive high strength materials, also increasing costs.
Increased downhole operating loads and costs are pushing the limits of current axial disconnects. Therefore, a stronger axial disconnect that does not resort to expensive materials is desirable. Stronger axial disconnects that also have few working parts, and thus ease manufacturing, installation, or operational complexities and related costs, would likewise be desirable.